The transmission/reception of signals between devices is stable in wired signal transmission. The signal transmission rate is increasing year after year, and transmitting high frequency signals in the EHF band over a wire is being put into practice. The signal transmission medium used for transmitting signals between devices therefore needs to be capable of handling signals with increased transmission rates as well. In addition to simple signal transmission between two devices, signal transmission media are used in, for example, an evaluation of the characteristics of a semiconductor chip that processes EHF band high frequency signals, for the purpose of connecting the semiconductor chip to be evaluated and a measuring apparatus.
A measurement system for measuring high frequency signals in an evaluation of a semiconductor chip includes, for example, a measuring apparatus whose measurement port includes a waveguide with a flange, and a signal transmission medium. The signal transmission medium includes a transmission line portion which has at one end a probe head provided with a probe tip to be brought into contact with a device to be evaluated and which has at the other end a connector for connecting to the flange of the waveguide. A coaxial cable, a waveguide, a strip line or the like can be used for the transmission line portion.
Coaxial cables are advantageous in structuring the measurement system with relatively less restriction due to their flexibility and ease of wiring. However, the transmission of 110 [GHz] signals, for example, requires a coaxial cable sized 0.4 [mm] or less in the outer diameter of the center conductor and 1 [mm] or less in the inner diameter of the outer conductor. Realizing a coaxial cable of this fineness is difficult from the standpoint of machining accuracy. For that reason, coaxial cables that can be used for 110 [GHz] or higher do not exist at present.
Waveguides and strip lines are superior to coaxial cables in term of the transmission of high frequency signals. However, since waveguides are inflexible and limit the structuring of the measurement system, the measurement system cannot be freely structured. With strip lines, since dielectric substances, which are indispensable to strip lines, increase loss, the increased loss makes accurate measurement difficult.
Thus, there are currently no signal transmission media on the market that are optimum for the transmission of high frequency signals such as EHF band signals between two devices.
Patent Literature 1 and Patent Literature 2, cited below, disclose inventions pertaining to a conventional signal transmission medium used in the measurement system described above. Both inventions are aimed for the transmission of high frequency signals and use as the transmission line portion a strip line that has a probe head at one end. In Patent Literature 3, cited below, a coaxial cable having a probe head at one end is used as the transmission line portion.
Suspended strip lines have been proposed as strip lines that are favorable for the transmission of high frequency signals. An example of suspended strip lines is introduced in Non Patent Literature 1, cited below. Suspended strip lines are said to be superior to conventional strip lines in terms of high Q-factor, wide bandwidth, characteristics stability with respect to temperature, and other points. The suspended strip line introduced in Non Patent Literature 1, cited below, however, is inflexible and therefore limits the structuring of the measurement system.